The overall objective of this project is to gain understanding of the physical-chemical mechanism of the reactions between proteins and nucleic acids. We use, as a model system, the regulatory interactions of the lac operon of E. coli. While the mode of action of lac repressor is fairly well understood, the mechanism by which the cAMP receptor protein, CAP, stimulates transcription is entirely obscure. Our immediate goal is to characterize the specific binding of purified CAP protein to the lac promoter. We will also examine the possible effect of CAP binding on the stability of the repressor-operator complex located approximately 50 base pairs away.